The object of this proposal is to continue investigating the effects of electrical and/or magnetic fields on epiphyseal plate growth in order to determine the feasibility of stimulating shortened extremities in children. The proposed investigation is designed (1) to determine the electrical and/or magnetic parameters required to produce maximum epiphyseal plate growth as measured by photomacrography, 3H-thymidine, 35S, 14C-proline, and 45Ca uptake and metaphyseal tetracyclin labeling using in vitro and in vivo models; (2) to define regulation of epiphyseal plate growth and differentiation in normal and electrically stimulated in vitro models by correlating intracellular concentrations of cAMP and cGMP with 3H-thymidine, 35S, 14C-proline, and 45Ca uptake, with hydroxyproline, hexosamine, DNA, and protein content, and with ash weight, and by noting the effect of the addition of cyclic nucleotides in the media on the above parameters; (3) to determine the mitochondrial calcium uptake and release characteristics in the presence and absence of an electrical field; (4) to quantitate the ultrastructural changes in cytoplasmic components of chondrocytes exposed to an electrical field, and (5) to quantitate changes in the negative surface charges of electrically stimulated chondrocytes and to correlate these changes with alterations in chondrocyte cAMP and cGMP.